| ??? 04/01/10 07:14 Modified: 04/01/10 07:15 Read: times |
#174713 - Good question.. Responding to: ???'s previous message |
Andy Neil said:
Valentin Angelovski said:
MOV DPTR, #1000h CLR A MOVC A, @A+DPTR What's the point of the CLR A ? Hi Andy, A good question! Reason we zero the accumulator, is to remove the 'pointer offset' that is introduced into the subsequent MOVC instruction.. Say, for example the 'CLR A' opcode directive was removed from the above example and acc initially contained 32hex.. Upon execution of the MOVC instruction, data would be fetched from 1032h, instead of 1000h as originally intended! Cheers, Valentin |
| Topic | Author | Date |
| 8051 Instruction MOV A, addr | 01/01/70 00:00 | |
| If reading from codespace, use 'MOVC' | 01/01/70 00:00 | |
| Why CLR A ? | 01/01/70 00:00 | |
| Good question.. | 01/01/70 00:00 | |
| I must be going blind! | 01/01/70 00:00 | |
| re | 01/01/70 00:00 | |
| Did you check the so-called "bible"? | 01/01/70 00:00 | |
| I should have clarified | 01/01/70 00:00 | |
external | 01/01/70 00:00 | |
| reply to re | 01/01/70 00:00 | |
| CLR A?? | 01/01/70 00:00 | |
| "bible" time | 01/01/70 00:00 | |
| Done :-) | 01/01/70 00:00 | |
| "bible" time | 01/01/70 00:00 |